This invention relates to a height adjustment for the back rests of chairs, especially of office swivel chairs.
Screw-clamping devices are known for adjusting the height of a back rest that comprises a back plate (which may be padded) connected to a fastening element that slides lengthwise on a back rest carrier, where the back rest carrier and the fastening element are clamped together.
Several prior inventions have tried to increase the ease of operation of such a height adjusting mechanism, for example, by having a sitting person adjust the back rest with a hand wheel and a spindle (German patent DE-A-39 39 321). Another example shows the clamping of a slideable bar that carries the back rest with two pivotably mounted angle irons prestressed by a tension spring, so that the angle irons are clamped contiguously to recesses of the bar and can be disconnected from the bar by means of a push-button (German patent DE-A-22 18 894). None of the existing devices are satisfactory.